Vapor solvent paint removing method

ABSTRACT

A METHOD IS DISCLOSED FOR REMOVING PAINT FROM METAL SURFACES BY BOILING A SOLVENT OR SOLVENT MIXTURE AND CONTACTING THE PAINTED METAL SURFACE WITH THE VAPORS OF THE SOLVENT MIXTURE.

United States Patent US. Cl. 13431 7 Claims ABSTRACT OF THE DISCLOSURE A method is disclosed for removing paint from metal surfaces by boiling a solvent or solvent mixture and contacting the painted metal surface with the vapors of the solvent mixture.

This application for US. Letters is a division, of application Ser. No. 148,213, filed May 28, 1971, now US. Pat. No. 3,743,542 which is a divisional of US. Ser. No. 817,160, filed Apr. 17, 1969, now US. Pat. No. 3,629,004.

This invention relates to a method for removing paint from metal surfaces by stripping with solvent vapors.

Paint stripping methods using liquid and paste compositions are well known in the art. Typically, the painted surfaces are immersed into hot alkaline baths for paint removal while in other instances a liquid or paste remover is applied to the painted surfaces and the treated paint is removed mechanically by scraping or the like. With some liquid and paste paint removers, the treated paint can be removed by washing.

Very adherent, durable paints and coatings based upon chemically resistant resins such as vinyl, acrylic, epoxy resins or the like have been developed which present a unique problem for conventional paint removal compositions. Although paint strippers have been developed for these durable paints, they have not proven entirely satisfactory from the standpoint of efficient, rapid, removal of such paints. Typically, these compositions require prolonged periods of treatment for complete stripping. The use of aqueous alkali solutions containing phenolic compounds such as cresylates have been employed as hot tank strippers with little commercial acceptance because of the disposal difliculty associated with phenolics.

It has now been found that by the practice of this invention, a method is provided for removing paint from metal surfaces by treating the paint with a solvent vapor which greatly facilitates paint removal. The present method is especially useful for removal of durable paints such as those based on vinyl, acrylic, or epoxy resins.

This invention, generally stated, involves a method for removing paint from metal surfaces by boiling a solvent or solvent mixture for the paint and contacting a metal surface coated with paint with a solvent vapor.

In the method of this invention, the paint stripping solvent or solvent mixture is heated to its boiling point and the painted metal surface is contacted with the vapors. The method is preferably carried out in a closed system to prevent loss of vapors and for safety purposes. An apparatus having the structure of a vapor degreasing machine may be used for this purpose if desired. The stripping apparatus preferably has a portion of the outside enclosed with cooling coils to provide a continuous refluxing of the solvent vapors. The particular apparatus employed, however, is not critical to the practice of this invention.

The method of this invention may be used for removing paints from a wide variety of metals including ferrous,

. copper, aluminum and like metals and their alloys. The

paints which may be removed by this method include varnishes, enamels, lattices, emulsion coatings and the like. Conventional drying oil base paints, acrylic base paints, epoxy base paints, phenolic base paints, and rubber base paints may also be effectively removed. This method is particularly suitable for removing acrylic and epoxy base paints from ferrous metal surfaces such as steel.

The volatile solvents which may be used in the practice of the present invention include chlorinated liquid hydrocarbons, hydrogenated aromatic solvents, saturated heterocyclic compounds, surface active agents, imidazole derivatives, alkynyl, alcohols, glycol ethers, carboxylic acids, ethanolated alkyl guanidine amine complexes, and ali phatic alcohols.

Chlorinated liquid hydrocarbons found useful herein include methylene chloride, trichloroethylene, perchloroethylene, trichlorobenzene, orthodichlorobenzene and the like.

Hydrogenated aromatic solvents found useful herein include tetrahydronaphthalene and the like.

Saturated heterocyclic compounds found useful herein include compounds containing nitrogen, oxygen, or both nitrogen and oxygen in the basic structure such as morpholine, N-methyl morpholine, thiomorpholine, dioxane, tetrahydrofuran and the like.

Surface active agents found useful herein include alkyl benzene sulfonic acid where the alkyl group includes from about 8 to about 18 carbon atoms such as dodecyl benzene sulfonic acid.

Imidazole derivatives found useful herein include materials such as those sold under the trade name Miranol CS, an alkyl(coco) ethyl cycloiminidium l-hydroxy 3- ethanol 2-isopropyl sodium sulfonate; Miranol IS, an alkyl (octoic) ethyl cycloiminidium l-hydroxy, 3-ethanol 2-isopropyl sodium sulfonate; or the like.

Miranols are synthetic detergents disclosed in US. Pats. Nos. 2,528,378 and 2,773,068 (incorporated herein by reference) and have the formula wherein R is a hydrocarbon radical having from 4 to 18 carbons, R is a hydrocarbon radical having from 1 to 4 carbons, R CO is an acyl radical having from 1 to 4 carbons, X is H, Na, K, -CH COONa, CH CO0K or -CH COOH, and Y is H, Na, or K.

Alkynyl alcohols found useful herein are exemplified by 3,5-dimethyl-1-hexyn-3-ol and the like.

Glycol ethers found useful herein include materials such as ethylene glycol monomethyl ether, ethylene glycol monethyl ether, ethylene glycol phenyl ether, propylene glycol methyl ether, and ethoxytriglycol or the like.

Carboxylic acids found useful herein are those having 1 to about 4 carbon atoms and include formic acid, acetic acid, propionic acid, and butyric acid.

Ethanolated alkyl guanidine amine complexes usefully employed herein include materials such as that sold under the trade name Aerosol 61 (an ethylene oxide adduct of octadecyl quanidine-amine complex), or the like.

Aliphatic alcohols found useful herein include alcohols such as methyl isobutyl carbinol and the like.

Mixtures of useful solvents may also prove useful in the practice of the present invention. For example, mixtures of about 10 to about parts by Weight morpholine with correspondingly about 90 to about 10 parts by weight of a solvent selected from the group consisting of chlorinated liquid hydrocarbons, hydrogenated aro-' matic hydrocarbons, glycol ethers and mixtures thereof have been found useful. Mixtures of about to about 90 parts by weight of a chlorinated hydrocarbon selected from the group consisting of methylene chloride and perchlorethylene with correspondingly about 90 to about 10 parts by weight of solvents selected from the group consisting of alkyl benzene sulfonic acids, lower aliphatic alcohols and their glycol ethers, alkynyl alcohols, hydrogenated aromatic hydrocarbons, carboxylic acids containing 1 to 4 carbon atoms, imidazole derivatives, ethanolated quanidine amine complexes and mixtures thereof may also prove effective in the practice of the present invention.

The compounds of this invention have been found to give the greatest penetration and stripping properties for acrylic enamels. Almost complete paint removal without any mechanical treatment has been observed.

In order to further illustrate the present invention, the following examples are given wherein all parts are by weight unless otherwise indicated.

EXAMPLE 1 Paint hooks having 4 inch long sections coated with A3 inch thick Jones Dabney polymerized acrylamide paint accumulation were placed over beakers containing 83 parts by weight methylene chloride, 10 parts by weight of 90% formic acid, and 1 part by weight of an imidazoline surfactant having the following formula:

This formulation appeared as a clear, amber mixture which boiled at 104 F. The paint hooks were exposed to vapors of this formulation for about 30 minutes after which time loose accumulated paint was brushed off. The hooks were re-exposed to vapors of this formulation for minutes and about 98% of the paint accumulation was removed. When hooks having this accumulation of paint are processed by hot tank alkaline stripping methods, a period of up to 4 hours is usually required for comparable paint removal.

EXAMPLE 2 Paint hooks having 4 inch long sections coated with M; inch thick Jones Dabney polymerized acrylamide paint accumulation were treated to remove the paint. The hooks were placed over beakers containing a mixture of 50 parts by weight morpholine and 50 parts by weight tetrahydronaphthalene. Vapors of this mixture from a solvent boiling temperature of 104 F. were contacted with the accumulated paint. The effect of the vapor penetration was readily evident. After a 60 minute interval, the paint had been 90% removed. Usually this accumulation of paint requires 3 to 4 hours for complete removal by using hot tank alkaline stripping methods.

EXAMPLES 3-17 The procedure of Example 2 was repeated with paint hooks having similar paint accumulation thereon. The time of exposure varied from 15 to 35 minutes using the following formulations in amounts indicated:

EXAMPLE 3 Ingredients: Parts by weight Methylene chloride 83 Formic acid (90%) 10 Imidazoline surfactant of Example 1 1 Linear dodecyl benzene sulfonic acid 6 4 EXAMPLE 4 Ingredients: Parts by weight Methylene chloride 73 Formic acid (90%) 10 Linear dodecyl benzene sulfonic acid 1 Ethylene glycol phenyl ether 10 EXAMPLE 5 Ingredients: Parts by weight Methylene chloride Formic acid 10 Ethylene glycol phenyl ether 6 Guanidine amine complex 4 EXAMPLE 6 Ingredients: Parts by weight Methylene chloride 80 Formic acid (90%) 11 Ethylene glycol methyl ether 8 3,5 Dimethyl-1-hexyn-3-01 1 EXAMPLE 7 Ingredients: Parts by weight Methylene chloride 63.76 Formic acid (90%) 17 Imidazoline surfactant of Example 1 6 Linear dodecyl benzene sulfonic acid 6 Perchloroethylene 11.25

EXAMPLE 8 Ingredients: Parts by weight Morpholine 10 Orthodichlorobenzene 90 EXAMPLE 9 Ingredients: Parts by weight Moropholine 10 Ethoxytriglycol 90 EXAMPLE 10 Ingredients: Parts by weight Morpholine EXAMPLE 11 Ingredients: Parts by weight Methylene chloride 90 Methyl-iso-butyl-carbinol 10 EXAMPLE 12 Ingredients: Parts by weight Methylene chloride 90 Tetrahydronaphthalene 10 EXAMPLE 13 Ingredients: Parts by weight Methylene chloride 50 Tetrahydronaphthalene 50 EXAMPLE 14 Ingredients: Parts by weight Methylene chloride 47.6 Formic acid (90%) 48 Tetrahydronaphthalene 47.6

EXAMPLE 15 Ingredients: Parts by weight Methylene chloride 77.5 Formic acid (90%) 10 Linear dodecyl benzene sulfonic acid 2.5 Tetrahydronaphthalene 10 EXAMPLE 16 Ingredients: Parts by weight Methylene chloride 38.75 Formic acid (90%) 5 Linear dodecyl benzene sulfonic acid 1.25 Tetrahydronaphthalene 55 EXAMPLE 17 Ingredients: Parts by weight Morpholine 50 Tetrahydronaphthalene 50 EXAMPLE 18 I 4" x 6" steel panels having four coats of Pittsburgh Plate Glass Duracor 100 acrylic paint in addition to an epoxy primer were treated to remove the paint accumulation. The steel panels were placed over beakers containing a mixture of 73 parts by weight methylene chloride, parts by weight of 90% formic acid, 7 parts by weight of linear dodecyl benzene sulfonic acid and 10 parts by weight ethylene glycol phenyl ether. Vapors of this mixture were contacted with the accumulated paint. The elfect of the vapor penetration was immediately evident. After an interval of 17 minutes, from 95-98% of the paint was removed from the steel panels. Usually this accumulation of paint requires 60 minutes by using the most effective hot tank alkaline stripping methods.

EXAMPLES 19-26 The procedure of Example 18 was repeated with steel panels having similar paint accumulation thereon. The time of exposure varied from to 30 minutes using the following formulations in amounts indicated:

EXAMPLE 19 Ingredients: Parts by weight Perchlorethylene 50 Ethylene glycol methyl ether 50 EXAMPLE 20 Ingredients: Parts by weight Perchlorethylene 33 Ethylene glycol methyl ether 33 Morpholine 33 EXAMPLE 21 Ingredients: Parts by weight Perchlorethylene 70 Ethylene glycol methyl ether 10 Methylene chloride 20 EXAMPLE 22 Ingredients: 3 Parts by weight Methylene chloride 80 Formic acid (90%) 10 Propylene glycol 10 EXAMPLE 23 Ingredients: Parts by weight Methylene chloride 74.5 Formic acid (90%) 9.3 Water 3.7 Linear dodecyl benzene sulfonic acid 7.0 Imidazoline surfactant of Example 1 5.5

EXAMPLE 24 Ingredients: Parts by weight Methylene chloride 60 Formic acid (90%) 20 Propylene glycol methyl ether 10 Linear dodecyl benzene sulfonic acid 10 EXAMPLE 25 Ingredients: Parts by weight Methylene chloride 75 Formic acid (90%) 10 Propylene glycol methyl ether 8 Linear dodecyl benzene sulfonic acid 7 6 EXAMPLE 26 Ingredients: Parts by weight Methylene chloride 73 For-mic acid (90%) 10 Linear dodecyl benzene sulfonic acid 7 Ethylene glycol phenyl ether 10 In all of the above instances of Examples 19-26, 85% to 98% of the paint accumulation on the panels was removed.

EXAMPLE 27 Paint hooks having 4 inch long sections coated with A inch accumulation of Glidden acrylic paint were treated for paint removal. These hooks were placed over beakers containing a mixture of parts by weight methylene chloride and 20 parts by weight 90% formic acid. Vapors of this mixture were contacted with the accumulated paint. The eifect of the vapor penetration was readily evident. After a 20 minute interval, -90% of the paint accumulation was removed from the metal hooks. Usually, this accumulation of paint requires several hours for comparable paint removal by using hot tank alkaline stripping methods.

EXAMPLE 28-30 The procedure of Example 27 was repeated with paint hooks having similar paint accumulation thereon. The time of exposure varied from 20 to 30 minutes using the following formulations in amounts indicated:

EXAMPLE 28 Ingredients: Parts by weight Perchlorethylene 36.4 Methylene chloride 36.4 Formic acid 18.2 Linear dodecyl benzene sulfonic acid 9.0

EXAMPLE 29 Ingredients: Parts by weight Perchlorethylene 30 Methylene chloride 50 Di-tri-isopropanolamine 20 EXAMPLE 30 Ingredients: Parts by weight Methylene chloride 80 Formic acid (90%) 10 Propylene glycol methyl ether 10 In all of the above instances of Examples 28-30, 85% to 98% of the paint accumulation on the hooks was removed.

EXAMPLE 31 Paint hooks having 4 inch long section coated with A to /2 inch accumulation of Ford Automative J-32 Acrylic paint were treated for paint removal. These hooks were placed over beakers containing a mixture of 36.4 parts by weight erchloroethylene, 36.4 polychlorobenzene, 9 parts by weight linear dodecyl benzene sulfonic acid, and 18.2 parts by weight of 90% formic acid. Vapors of this mixture were contacted with the accumulated paint. After 3-4 minutes, 85-90% of the paint had been removed. The usual time required for complete stripping of Ford Automotive J-32 Acrylic paint ranges up to 32 hours by using hot tank alkaline stripping methods.

EXAMPLES 32-34 EXAMPLE 32 Ingredients: Parts by weight Perchloroethylene 90 Morpholine 10 EXAMPLE 33 Ingredients: Parts by weight Perchloroethylene 80 Linear dodecyl benzene sulfonic acid 20 EXAMPLE 34 Ingredients: Parts by weight Perchloroethylene 50 Ethyoxytriglycol 50 In all of the above instances of Examples 32-34, 75% to 100% of the paint accumulation was removed.

It is understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from this invention.

What is claimed is:

1. A method for removing paint from a metal surface which comprises, heating a volatile paint solvent to boiling, contacting the painted metal surface with vapors of the heated paint solvent, and thereafter removing at least a substantial amount of the paint from the meal surface, said volatile solvent being a mixture of about to about 90 parts by weight of a chlorinated hydrocarbon selected from the group consisting of methylene chloride and perchlorethylene with correspondingly about 90 to about 10 parts by weight of a solvent selected from the group consisting of alkyl benzene sulfonic acids, lower aliphatic alcohols and their glycol ethers, alkynyl alcohols, hydrogenated aromatic hydrocarbons, carboxylic acids containing 1 to 4 carbon atoms, imidazole derivatives, ethanolated guanidine amine complexes and mixtures thereof.

2. A method for removing paint from a metal surface which comprises, heating a volatile paint solvent to boiling, contacting the painted metal surface with vapors of the heated paint solvent, and thereafter removing at least a substantial amount of the paint from the metal surface, said volatile solvent being formed of 80 parts by weight of a first component selected from the group consisting of perchloroethylene, and methylene chloride; and 20 parts by weight of a second component selected from the group consisting of 90% formic acid and linear dodecyl benzene sulfonic acid.

3. A method for removing paint from a metal surface which comprises, heating a volatile paint solvent to boiling, contacting the painted metal surface with vapors of the heated paint solvent, and thereafter removing at least a substantial amount of the paint from the metal surface, said volatile solvent being formed of 80 parts by weight methylene chloride, 10 parts by weight of 90% formic acid, and 10 parts by weight of a member selected from the group consisting of propylene glycol methyl ether, ethylene glycol phenyl ether, guanidine amine complex, propylene glycol or mixtures thereof.

4. A method for removing paint from a metal surface which comprises, heating a volatile paint solvent to boiling, contacting the painted metal surface with vapors of the heated paint solvent, and thereafter removing at least a substantial amount of the paint from the meal surface, said volatile solvent being formed of parts by weight methylene chloride, 11 parts by weight formic acid 8 parts by Weight ethylene glycol methyl ether, and 1 part by weight 3,5-dimethyl-1-hexyn-3-ol.

5. A method for removing paint from a metal surface which comprises, heating a volatile paint solvent to boiling, contacting the painted metal surface with vapors of the heated paint solvent, and thereafter removing at least a substantial amount of the paint from the meal surface, said volatile solvent being formed of 60 parts by weight methylene chloride, 20 parts by Weight formic acid (90% 10 parts by weight propylene glycol methyl ether, and 10 parts by weight linear dodecyl benzene sulfonic acid.

6. A method for removing paint from a metal surface which comprises, heating a volatile paint solvent to boiling, contacting the painted metal surface with vapors of the heated paint solvent, and thereafter removing at least a substantial amount of the paint from the metal surface, said volatile solvent being formed of 30 parts by weight of perchlorethylene, 50 parts by Weight of methylene chloride, and 20 parts by Weight of di-tri-isopropanolamine.

7. A method for removing paint from a metal surface which comprises, heating a volatile paint solvent to boiling, contacting the painted metal surface with vapors of the heated paint solvent, and thereafter removing at least a substantial amount of the paint from the metal surface, said volatile solvent being formed of about 73-75 parts by weight of methylene chloride, 10 parts by weight of 90% formic acid, 7 parts by weight of linear dodecyl benzene sulfonic acid, and about 8-10 parts by weight of a member selected from the group consisting of propylene glycol methyl ether and ethylene glycol phenyl ether.

References Cited UNITED STATES PATENTS 608,948 8/1898 Barnard et al 134-3l X 2,279,267 4/1942 Kremers 1343,8 UX 2,689,198 9/1954 Judd 134'31 X 2,956,911 10/1960 Jelen 134-22 R M. S. ALVO, Assistant Examiner S. LEON BASHORE, Primary Examiner US. Cl. X.R.

13411, 38; 252162, 170, 171, Dig. 008 

